Klaus D. Schmidt (born 25 September 1943) is an Austrian mathematician and retired professor at the Faculty of Mathematics, University of Vienna.

After studying mathematics at the University of Vienna he received his doctorate in 1968 under Edmund Hlawka.

In 1975/76 K. R. Parthasarathy invited Klaus Schmidt to spend 7 months at the new Delhi Centre of Indian Statistical Institute (Parthasarathy was then working at the Indian Institute of Technology, Delhi).

In 1994 he was awarded the Ferran Sunyer i Balaguer Prize for the monograph Dynamical systems of algebraic origin.

He has researched among other things, ergodic theory and its connections with arithmetic, commutative algebra, harmonic analysis, operator algebras and probability theory.